This invention concerns counter-rotating gas turbines having a heat exchanger in the turbine flow duct. It is widely known to use heat exchangers (recuperators) in the flow duct of gas turbine engines (Paul Graig, in Electric and Hybrid Vehicle Design Studies, SP 1243, Society of Automotive Engineers, Inc., 1997, Warrendale, Pa., p. 135). The heat exchangers are used to increase efficiency by recycling waste heat. Normally, the heat exchanger is mounted outside the gas turbine engine and is connected to it by means of piping, or, as is the case with the above reference, the heat exchanger encloses the gas turbine engine and has an outer annular casing wall that can be heat insulated on the outside to lower heat losses to the ambient environment. Normally, the gas turbine engine has a separate frame that supports the turbine stator, the combustor and the shaft bearings. The outer annular wall or casing of the heat exchanger is supported by the frame and is hot during operation.
It is also known to use counter-rotating gas turbine engines (see our pending application Ser. No. 09/161,170, filed Sep. 25, 1998) in which a turbine and a compressor turbine rotate on different shafts in opposite directions, and shafts are journalled in bearings. The gas turbine engine has a heat exchanger that is used to heat the fluid coming from the compressor to the combustor and to the turbine. It should be noted that in the gas turbine engine of this type, there is no stator with guide vanes, and the compressor turbine is mounted immediately downstream of the turbine, and the turbine functions as a rotating guide vane system for the compressor turbine. This means that the fluid from the turbine flows directly to the blades of the compressor turbine. Therefore, the flow duct between the two turbines must have a stable geometry to minimize losses. This means that the clearance between the two turbines and the position of their shafts in space (alignment) should be maintained as accurate as possible under any operating conditions (speed, power, and temperature). Any deviation from the accurate geometry between the two turbines will result in a decrease in efficiency.